The present invention relates to a four-sided insert for milling cutters with negative radial angle of the cutting edges for three-dimensional milling from the solid. In particular, the invention relates to a four-sided insert to be mounted on a milling cutter with a registration angle χ, i.e., the angle between the main active cutting edge and the front surface, of substantially 90°, with a highly negative radial angle re for three-dimensional milling of slots from the solid, i.e., without having to form a pre-bore beforehand. Moreover, in the insert according to the invention it is possible to use all the faces of the insert as cutting edges.
As is known, in milling cutters a highly negative radial angle re is used mainly to allow the production of milling cutters that have a large number of cutting edges while maintaining high strength in the region underlying the insert and in order to facilitate manufacturing and reduce its cost.
Four-sided inserts currently used to mill recesses are generally diamond-shaped. They have two opposite long sides, which constitute the main cutting tips (commonly known as cutting edges), and two short sides, which constitute the secondary cutting edges. The point, or rather the region, where a long cutting edge and a short cutting edge meet is the tip of the cutting edge (outer tip). Particular care is given to the shape of this region, since it is important in order to achieve some of the goals of the machining process, such as for example the quality of the milled surface and the strength of the tip proper, while no particular care is given to the opposite end of the short side (inner tip) because it is not used in cutting.
Inserts of this kind are well-suited for face milling or climb milling, but for ramp milling, i.e., for three-dimensional milling, they require use on milling cutters with a radial angle re of the cutting edges that is substantially positive or nil.
In order to perform ramp milling, inserts have been designed which have a small protrusion or tooth at the region of the secondary cutting edge that joins the tip of the cutting edge (outer tip). However, this refinement allows to perform only ramp milling operations with very shallow inclinations, unless a pre-bore is produced which allows to engage in cutting only a portion of the secondary cutting edge, leaving free the end (inner tip) of the secondary cutting edge that lies opposite the tip of the cutting edge (outer tip). This accordingly prevents milling from the solid. Moreover, the presence of the tooth greatly limits the possibility to use on another milling cutter the short side as a peripheral cutting edge, thus halving the possibility to use the insert.